Higher alkylene glycol esters of alginic acid



am QS A, B sTElNER ETAL ,494,92

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FIG. 4

FIG.5

ARNOLD B. STEINER W. H. McNEE'LY NvENToRs Patented Jan. 17, 1950 HIGHERALKYLENE GLYCOL ESTERS OF ALGINIC ACID Arnold B. Steiner, La. Jolla, andWilliam H. Mc-

Neely, San Diego, Calif., assignors to Kelco Company, San Diego, Calif.,a corporation of Delaware Application January 20, 1947, Serial No.723,116 1o claims. (ci. 26o-209.6)

This invention relates to reactions` between alginic acid and certain ofthe epoxyparalns or alkylene oxides by which the properties of the acidare changed in a manner which imparts a new utility to the product.

This invention relates also to the products of the above recitedreactions, these products having the desirable properties of thewater-soluble salts and lower esters of alginic acid, together withcertain other useful properties which these compounds do not possess.

In a copending application led April 3, 1944 by Arnold B. Steiner underSerial No. 529,423, now Patent 2,426,125, it is disclosed that alginicacid may be reacted directly with alkylene oxides containing not morethan ve carbon atoms to form a theretofore unknown series of additioncompounds which have been termed glycol alginates. These compoundsdiffer from alginic acid and from the water-soluble alkali metalalginates in the following respects.

Alginic acid is substantially insoluble in water; its salts with thealkali metals, magnesium, ammonium and many organic bases are freelywatersoluble, yielding colloidal solutions of high viscosity. The glycolalginates likewise are freely water-soluble and form viscous andcolloidal solutions.

The soluble salts of alginic acid above described form gels orgelatinous precipitates with the water-soluble salts of thealkaline-earth metals (except magnesium) oi-aluminum andof the heavy theranges are upward from pH 5 with the alginic.

salts and downward from pH `5 in the case of the esters.

The reaction between alginic acid and the lower epoxyparafns (fivecarbon atoms or less) takes place with considerable readiness. Asdisclosed in the above copending application, a moist alginic acid iniibrous or other'subdivided form is treated with the alkylene oxide in aclosed vessel, the reaction usually coming to completion in from one tothree hours.A The product retains the brous form (unless a large excessof water be present) and appears in the original degrec of comminuation.No further preparation is required other than to evaporate or extractany excess oxide which it may contain and to bring the water content toa standard.

weight of the oxide increases.

More diiiiculty was found in reacting alginic acid with the higheroxides (six to eighteen carbon), the diiiculty increasing as themolecular The reaction becomes slower, esterication is less complete,the yield is smaller and the essential property of water solubility isnot fully developed when methods previously described are used.

We have now discovered that these diiilculties may be avoided and asatisfactory yield of products of high emulsifying value obtained bycertain/modifications of the original process, to wit:

(a) By the partial neutralization of the alginic acid prior toesterication, as disclosed in the copending application of Arnold B.Steiner and William H. McNeely, iiled December 22, 1945 under Serial No.636,938;

(b) By reacting the alginic acid with the higher oxide in the presenceof a water-miscible solvent such as acetone, glycerol or one of thelower aliphatic alcohols; or

(c) By reacting the alginic acid with a higher oxide and again reactingthe primary product with one of the lower oxides; or

(d) By reacting the alginic acid with a higher oxide, preferably in thepresence of a solvent, freeing the reaction product from the glycolformed as by-product, and repeating the treatment with the higher oxide,this alternative being most eiilcacious in the use of oxides from C6 toC8.

These various steps and the products resulting therefrom are describedwith reference to the structural diagrams of the attached drawings. inwhich Fig. l illustrates the known structure of alginic acid;

Fig. 2 shows the known result of complete neutralization of the carboxylgroups of alginic acid with sodium;

Fig. 3 shows the probable structureof a product resulting from thecomplete esteriilcation of alginic acid with an alkylene oxide RO, whereR represents any CnHzn alkylene group;

Fig. 4 represents the probable structure of the product resulting fromthe partial neutralization of the acid followed by incompleteesteriflcation of the remaining carboxyl groups, and

Fig. 5 shows the probable structure of a product in which the carboxylof one u'nit of the alginie acid has been satisiled with sodium, anotherwith a higher alkylene oxide RO, and a third with a lower alkylene oxideRO.

It will be understood that all of these diagrams have been simplified byomitting any duplication of identical unit structures or linkages,alginic acid being a straight chain polymer which is often of extremelength. v

Alginic acid is known to consist essentially of anhydro-D-mannuronicacid residues linked glycosidically in accordance with the formula ofFig. 1. In this structure the mannuronic units are linked in such mannerthat the 4carboxyl groups are free to react while the aldehyde groupsare shielded by linkages. This diagram represents only two links in apolymeric chain which may contain from one hundred to several hundredunits.

The theoretical combining weight of alginic acid is the weight of oneanhydro-D-mannuronic unit or 176. The actual combining weight of thecommercial acid is nearer 215, indicating the presence of unknown,nontitratable substances. When alginic acid is combined with sodium inthe proportion (about) 215:23 the product is a neutral salt, thestructure being as in Fig. 2 which shows the carboxyl groups of the two(illustrative) mannuronic units satisfied by the base.

If it were possible to esterify alginic acid completely, the structureof the product would be as illustrated in Fig. 3, in which thereplaceable hydrogen of each carboxyl has attached to the oxygen of theoxide and through it to one of the carbons while the other carbons linkwith the terminal oxygen of the carboxyl. The validity of this structureis supported by the observation that alkalis decompose the ester,forming the salt of Fig. 2.

The alginic acid used as raw material may be produced by any vof themethods known in the prior art, preferably by a method such as that o fthe Thornley and Walsh Patent 1,814,981 which yields the free acid infibrous form. The acid need be only in a state of commercial purity yandpreferably contains a small proportion of calcium.

The free acid is first brought to the physical condition in which it ismost amenable to reaction .with the alkylene oxide. This involvesreduction of the original water content. which is of the order of 80%,to approximately 50% by weight. A desirable way of producing thisreduction is by repeated passage of the acid through a hammer millsupplied with a current of warm, dry air but any method of drying bygentle heating, evacuation or extraction with water-miscible solventsmay be used.

A water content oi' from 45% to 55%, while not critical, has` been foundto give the best reaction rate during esteriflcation with the leasthydrolysis of the alkylene oxide. 'I'he reduced water content alsostrongly facilitates subdivision, the product of the above combineddrying and shedding step being a fluffy mass of ne. thread-like breswhich expose a very large surface area per unit of mass.

The step of partial neutralization described in copending applicationSerial No. 638,938 is not essential to esteriication with thev higheroxides,

but it is highly desirable. The use of this step renders it possible tostabilize the product by raising its pH value above the critical leveloi' stability, reducing the number of free carboxyl groups in the ilnalproduct. It also facilitates the production of a fully soluble glycolalglnate, reduces the extent to which both the alginic acid and thealkylene oxide are hydrolized during the esterii'ying reaction, andmaterially accelerates the reaction between the oxide and the acid.

It is believed that when a quantity of a base insulcient for completeneutralization is added to the acid, it does not completely neutralize aportion of the acid molecules. leaving the remaining moleculesuncombined but, rather, that it distributes itself in such manner as tosatisfy a portion only of the carboxyl groups of each molecule. For thesame reason it appears probable that the remaining carboxyl groups ofeach molecule may be completely or partially blocked by esterification.The structure of the resultant product is believed to be as generallyindicated in Fig. 4.

In this figure the carboxyl of the first unit in the fragmental chainhas been satised with sodium, the second carboxyl remains unreactedwhile the third is esterifled with an alkylene oxide. In a chain havinga great number of units, each having one carboxyl group, bothneutralization and esterification may p'roceed by verysmall incrementsand the resultant product may have any percentage proportion o`f itscarboxyl groups combined with the base, or with the oxide. or l free,according to the extent to which each reaction is carried.

`Partial neutralization may be produced before. during or after thecompletion of the drying step. In general the method used is to reactthe acid with any base producing a water-soluble salt of the acid, asfor example ammonia, the lower amines or any of the basic compounds ofthe alkali metals or magnesium. The preferred base, which may b e usedin the 'form of the hydroxide. carbonate or phosphate, may convenientlybe reacted with the acid by mixing the acid with an alcoholic solutionor slurry of. the base. In reactions involving the lower oxides arelatively small portion of the carboxyl groups are thus satisfied butfor the higher oxide reactions we prefer to neutralize from 25% to 50%lof the carboxyl groups, thus hastening the esterication and improvingthe solubility of the ilnal product.

Alkylene oxides containing from six to eighteen carbon atoms may .beprepared by any of the methods described-in the literature. In theinstant experiments the method reported by Findvley et al. in TheJournal of the American Chemical Society, 67, page 412 (1945) wasfollowed. This method employs peracetic acid to vepoxidize thecorresponding olen to the 1,2-epoxyalkane. Thus, 1,2-epoxyhexane` wasprepared by reacting hexene-l with peracetic acid.

Regardless of the method of preparation, the higher oxides are sparinglysoluble in water, the solubility decreasing as the number of carbonatoms in the oxide chain increases. This in turn affects the reactivityof the oxide with alginic acid, the reactions being carried out.essentially in an aqueous medium. For example, when using finelydivided and partially neutralized alginic acid containing about 50%water, 1,2-epoxypropane esterifed approximately 70% of the carboxylgroups of the acid, 1,2-epoxyhexane esterifled only about 41% of thecarboxyls, 1,2epoxyhep tane about 25% and 1,2-epoxyoctane about 10%under the same conditions. y Increasing the excess of oxide in thereaction mixture does not noticeably improve the extent of esterifcationand it appears that the relative water solubility of the oxide is thelimiting factor.

This dimculty was overcome and the percentage esterication increased bythe addition to the reaction mass of a water-miscible solvent for theoxide, as for example acetone or glycerol. When acetone was added to thereaction mixture in an amount equal to that of water present, the percent esteriflcation increased from 10% to 24% in the case of1,2-epoxyoctane, while the substitution of glycerol in the sameproportion raised the esteriilcation percentage to 28%. The increasedesterication due to the addition of the mutual solvent is of majorimportance, in increasing the water-solubility of the product. Theesteriiled product of 1,2-epoxyoctane, for example, is insoluble inwater while the 24% and ,28% products are readily soluble, yielding`viscous colloidal solutions.

For the reaction of alginic acid with the higher oxides the contactingvessel should be in the nature of an autoclave. closed to prevent lossof vapor, and should be provided with eillcient stirring apparatus toinsure complete contact between solid and liquid. Means to control thetemperature, such as a jacket arranged for both heating and cooling,should be provided. 'Ihe iible temperature limits for esteriilcationappear to be about 35 and 70 C. while the indications are that theoptimum temperature lies wl the range 45 to 60 C., varying somewhat withother conditions.

The examples below indicate practical ways of edecting the reaction anddescribe the products obtained.

EXAMPLE l Preparation of heylene glycol alginate oist, commercialalginic acid was prepared for neutralization by suspending 1660 parts ofthe acid (300 parts dry weight) in 1100 parts isopropyl alcohol with veminutes stirring. A slurry of 31 parts trisodium phosphate in 600 partsalcohol was then added, this quantity being sumcient to neutralize about25% of the carboxyl groups of the acid. After thirty minutes stirringthe reaction product was drained, squeezed as dry as possible, shreddedby passing it through a hammer mill and dried for ve minutes at 130 F,The

. marcial acid at 215. The mixture was maintained at an internaltemperature of 40 C. for three Ahours and allowed to cool. Anotherequivalent (57 parts) of lthe oxide was then added and the reactioncompleted in three hours at an internal temperature of 50 C. Thereaction product, after cooling, was extracted with acetone to -recoverany excess oxide and any glycols which had formed and was dried forthirty minutes at 130 F.-

' The yield of hexylene glycol alginate was 142 parts, dry weight, or118% on the original anhydrous acid. The ester readily dissolved inwater to give a 11/4% solution of pH 3.4 and viscosity of 100centipoises. Neutralization and saponiiication showed that 34% of thecarboxyl groups in the product were free, 41% were esterifled and 25%were neutralized with sodium.

EXAMPLE 2 Preparation of heptylene glycol algnate llowing the procedureabove described, alginic acid (300 parts dry weight) was 35% neutralizedacid was added 238 parts (3 equivalents) oi' 1,2-epoxyheptane. Themixture was stirred tor seven hours at an internal temperature of 50 C.The reaction product was freed from excess oxide and from glycols byextraction with acetone and was dried for onehour at 130 F. i,

-The yield of the ester was 182 parts or 121% on the original acid.Neutralization and saponiilcation indicated that 40% of the carboxylgroups of the product were free, 25% were esteriiled and 35% werecombined with sodium. The product dissolved in water to give a 11,4%solution of pH 3.3V and a viscosity of 4600 centipoises.

lEXAMPLE 3 Preparation of octylene glycol alginate The following mixturewas reacted in an autoclave for eight hours at 50 C. and the reactionproduct extracted with isopropyl alcohol vand dried for forty-five.minutes at 130 F.

Parts Alginic acid, 25% neutralized, dry weight--- 150 Water carried byacid 163 Water added as such 87 Acetone 250 1,2-epoxyoctane (3equivalents) 270 The net yield of the ester was 152 parts or 101% on theoriginal'alginic acid. The carboxy groups in the product were 51% free,24% esteried and 25% neutralized. A 1%% solution of ,the product washazy but no insoluble specks or particles were observed. The pH of thesolution was 3.4 and the viscosity 100 centipoises.

Under the same conditions but with glycerol substituted for the acetonethe esterication of the carboxyl groups .was 28% and the solution oi theproduct had a pH ot 3.5.

' omitting both the acetone and the glycerol and using water as the solevehicle, the degree of esterincation was only 10% and' the reactionproduct was insoluble in water. l

- clave, rst for four hoursat 50 C., then for four hours at C. Thereaction product was extracted with isopropyl alcohol and dried for onehour at F.

. f Y Parts Alginlc acid, 25% neutralized. dry weiglit 150 Water1,2-epoxydecane (3 equivalents) 329 EXAMPLE 5 Preparation of dodecyleneglycol algmate The following mixture was reacted in an auto- 76 clavefor eleven hours at 50 C. and the reaction product lextracted and driedfor one hour at 130 F.

' Parts Alginic acid. 40% neutralized, dry weight 173 Water 150 Glycerol150 1,2-epoxydodecane (3 equivalents) 388 The yield of the ester, drybasis, was 216 parts or 125% on the original alginic acid.Saponiilcation showed that 39% of the carboxyl groups of the productwere free, 21% were esterified and 40% were combined with sodium. A-1%%aqueous solution of the product had a viscosity of 180 centipoises and3.2 pH.

EXAMPLE` s Preparation of octadecylene glycol alginate The followingmixture was reacted in an autoclave for four hours at 50 C. and forVeight additional hours at 55 C. The reaction product was extracted anddried for one hour at 130 C.

Parts Alginic acid. 50% neutralized 179 Water 153 Glycerol 1501,2-epoxyoctadecane (21A equivalents) 613 The yield of the ester, drybasis, was 283 parts or 158% of the original acid. The product had 33%of its carboxyl groups free, 17% esteried and 50% neutralized. A 1V4%solution had a viscosity of 110 centipoises and a pH value of 3.4.

EXAMPLE 7 Preparation of mixed glycol alginates Reaction productsapproaching complete esterication and having highly desirable propertiesmay be prepared by the method illustrated in this example, the productof reaction with one of the higher oxides being again acted on by anoxide of considerably lower molecular Weight.

A portion of the octylene glycol alginate product obtained in Example 3v(by reaction in the presence of acetone) was given three washes with acold, 50-50 water-alcohol mixture previously brought to pH 1.8 withhydrochloric acid. This treatment removes Ithe-sodium with which part ofthe carboxyls of the original product had been combined, rendering themagain available, for esteriication. This was followed by two washesvwith alcohol, and air drying.

The air dried product (75 parts dry weight) was placed in an autoclavetogether with water sufilcient to bring the water content to 50%. Ammo-Vshown to be free, 24% were esteried with the i octylene derivative and58% with the propylene derivative, and were combined with ammonia.

A large number of mixed esters may be formed in this general manner, bysubjecting the product o1' a trst reaction with one of the higher oxidesto a second reaction with one of the lower. Ordinarily, ethylene orpropylene oxide will be used for the second reaction, by reason of theavallability and low cost of the'se agents.

Reactions of products with heavy metal salts and with acids Thewater-soluble alginic salts (e. g., sodium and ammonium alginate) areextremely reactive with salts of the heavy metals and the alkalineearthmetals, giving gels or precipitates. The glycol alginates of the higheroxides are less reactive than the salts, while the glycol alginates withthe lower oxides are still less reactive.

For example, a sodium alginate solution gives a fibrous precipitate onthe additionof calcium chloride solution; the higher glycol alginatesyield hard gels, while the lower glycol alginates yield soft gels underthe same conditions.

Again, a solution of a propylene glycol alginate esterifled will not gelon the'additlon of a strong acid, while a solution of octylene ordecylene glycol alginate 20% esterifled will gel with a strong acid butnot with a weak acid such as acetic.

These differences in reactivity, however, are due to the lower` degreeof esteriiication producible with the higher oxides rather than to thelengthening of the hydrocarbon chain, and the reactivity falls offrapidly as percentage esteriiication increases. While a 70% esteriiiedpropylene glycol alginate is still somewhat reactive the mixed propyleneoctylene glycol alginate at only a slightly higher esteriiicationpercentage is completely nonreactive with alkaline-earths at pH 3.3 andis subject only to a slight thickening when mixed with calcium chloridesolution at pH 4.2.

In all cases the compatibility of the product with acids and withalkaline-earth metal salts improves as the degree of esterication isincreased, and for this reason the use of the watermiscible solventdescribed in Examples 3 and 5 is often highly advantageous. f

Selection and proportom'ng of solvent The presence of water is essentialto the reaction, which takes place between the solid acid and theaqueous solution of the alkylene oxide. At and above six carbon atoms inthe molecule the oxide becomes very sparingly water-soluble and reactionis correspondingly slow. Raising the temperature of reaction increasesits velocity but tends to degrade the acid (by depolymerization) whileincreasing the water content of the reaction mixture tends (as doeselevation of temperature) to increase the extent to which hydrolysis ofthe oxide to the corresponding glycol occurs.

The use of a mutual solvent accelerates the desired reaction betweenoxide andl acid by increasing the concentration of oxide in thesolution, and at the Sametime tends materially to restrain the undesiredhydrolysis ofthe oxide. For this purpose any organic liquid which isinert to alginic acid and to the oxide, which is a solvent for the oxideand which is soluble in water may be used. A wide variety of solventsare available for this purpose and a selection may be made from thegroup including the lower ketones and the lower monohydric andpolyhydric alcohols.

The 50-50 ratio of solvent to water used in these experiments is notcritical though it is generally satisfactory. The effect of the solventin promoting reaction appears to increase as the proportion increases,up to the point at which the hydrophilic solvent begins to shrink and9L. harden the acid ilbre by withdrawing water from it. With differentorganic solvents the optimum Water:solvent ratio may vary considerably,but the step is at least moderately elective within the limits 80waterz20 solvent to 30 water270 solvent.

Evaluation of emulsifying power of the product The major utility of theesters herein described is as emulsifying agents or, perhaps moreaccurately, as emulsion stabilizers. For this purpose the higher glycolalginates show to material advantage as compared with the lower, and tovery great advantage as compared with the water-soluble alginic saltssuch as sodium alginate.

The following quick-breaking test was devised for evaluating theemulsion stabilizing value of the product and is conducted as follows. A50% emulsion of a light mineral oil was made by adding the oil to awater sflution of the ester while stirring at 800 R. P. M. Theconcentration of the glycol alginate in each case was 0.6% of the weightof the completed emulsion. In order to eliminate variations in theviscosities of different esters, enough sodium alginate'was added toeach solution to bring the viscosity to about 100 centipoises. Thisaddition varied from 0.02% to 0.40% of the emulsion weight. To controlthe effect of pH the solution was titrated with sodium hydroxidesolution to bring the pH within the range to 6. Sodium benzoate. 0.2%.was added as a preservative.

After stirring the mixtures of oil and solution until thoroughly blendedthe emulsions were twice homogenized, using the same apparatus, speedand feed rate in each case. The homogenized emulsions were placed in 70x 25 mm. vials and stored at a constant temperature of 50 C., theseparation of oil from the bottom of the vial being noted at intervalsand recorded in millimeters. These results yielded curves from which thetime required to produce a 3 mm. break could be read with considerableaccuracy. The results thus obtained are tabulated below.

Emulsion stability test mm. break after storing for- Days for 3 mm.break Ester Used l day 2days days Propylene........ Hcxylene 1.Heptylenn Octylene. Decylcne. Octylene-P r o p yiene Sodium Alginate.2.0 Complete l/hour lit will be evident from these results that theesters above six carbon atoms in the alkylene chain, ranging from 41% to18% esterication, are materially more elective than the propylene esterat about 70% esteriflcation. The emulsifying value of sodium alginate inthis quick-breaking emulsion is negligible.

We claim as our invention:

l. The method of modifying alginic acid to render it water-soluble whichcomprises: treating said acid with a 1,2 alkylene oxide containing notless than six nor more than eighteen carbon atoms, in the presence ofwater and of a mutual solvent for water and for said oxide.

2. The method of modifying alginic acid lo render it water-soluble whichcomprises: treatilus said acid in the presence of water and of a 10mutual solvent for water and for the alkylene oxide with a 1,2 alkyleneoxide containing not less than six nor more than eighteen carbon atoms.and further treating the product of said treatment with a 1,2 alkyleneoxide containing not more than flve carbon atoms.

3. The product of reaction between alginic acid and a 1,2 alkylene oxidecontaining not less than six nor more than eighteen carbon atoms; asolid, alkylene glycol alginate characterized by su'bstantially completesolubility in water to form substantially clear, viscous, colloidalsolutions.

4. The product of reaction between alginic acid and a 1,2 alkyleneoxidecontaining not less than six nor more than eighteen carbon atoms: asolid, alkylene glycol alginate characterized by subl stantiallycomplete solubility in acidulated water to form substantially clear,viscous. colloidal solutions.

5. A solid, substantially completely water-soluble modification productof alginic acid in which a part of the carbonxyl groups of said acid areesterifed with a 1,2 alkylene oxide containing not less than six normore than eighteen carbon atoms. and a part of said carboxyl groups areesterifed with a 1,2 alkylene oxide containing not more than ve carbonatoms, said product characterized by fotming clear, viscous, colloidal.aqueous solutions.

6. The method of modifying alginic acid to render it water soluble whichcomprises: reacting said acid in the presence of water and of a mutualsolvent for water and the alkylene oxide with a 1,2 alkylene oxidecontaining not less than .six nor more than eighteen carbon atoms;freeing the reaction product from glycol formed as a byproduct of saidreaction, and reacting the glycol-free product, in the presence of waterand said solvent. with a 1,2 alkylene oxide containing not less than sixnor more than eghteen carbon atoms.

7.' The process of claim 1 wherein glycerol ls the solvent.

8. The process of claim 1 wherein acetone ls the solvent.

9. A substantially completely water-soluble long chain partial ester ofalginic acid in which part not to exceed about 41% of the carboxylgroups are esteried with a 1,2 alkylene oxide of 6 to 18 carbon atoms.said partial ester being furthel characterized by yielding clear,viscous colloidal solutions in water.

10. A substantially completely water-soluble long chain partial ester ofalginic acid in which about 17 to about 41% of the carboxyl groups areesterifled with a 1,2 alkylene oxide of 6 to 18 carbon atoms, about 25to about 50% of the carboxyl groups are reacted with a base, theremainder of said carboxyl groups being unreacted. said partial esterbeing further characterized by yielding clear, Viscous colloidalsolutions in water.

ARNOLD B. STEINER. WILLIAM H. MCNEELY.

REFERENCES CITED UNITED STATES PATENTS Name Date Steiner Aug. 19. 1947OTHER REFERENCES Malvezin, Chem. Zentr.. 1944, vol. I.. pages 757- 758.

Number

1. THE METHOD OF MODIFYING ALGINIC ACID TO RENDER IT WATER-SOLUBLE WHICHCOMPRISES; TREATING SAID ACID WITH A 1,2 ALKYLENE OXIDE CONTAINING NOTLESS THAN SIX NOR MORE THAN EIGHTEEN CARBON ATOMS, IN THE PRESENCE OFWATER AND OF A MUTUAL SOLVENT FOR WATER AND FOR SAID OXIDE.